The mystery remains to be solved, and researchers still can’t figure out the real reason why otters are playing stone juggling.

Otters have developed a habit that is difficult to crack scientifically, according to a new study by researchers at the University of Exeter. The study, published in the journal Open Science, the Royal Society, looked at the habit of stone-playing with otters and tried to explain the strange behavior. Unfortunately, the researchers didn’t find the answer.

The mystery remains to be solved, and researchers still can't figure out the real reason why otters are playing stone juggling.

Otters are not really sidesplaying, but they do throw stones around and play with them with astonishing dexterity. Scientists really want to figure out why. This behavior has been observed frequently by otters in captivity, although it is not clear if this is related.

The researchers involved in the study didn’t solve the big problem, but they didn’t come home empty-handed. The team came up with a clear link between otter sloothes and hunger, suggesting that animals tend to start performing their tricks when they feel hungry.

Middle-aged otters tend to play juggling more than younger or older otters, so researchers believe that juggling behavior may be related to the skills they use to eat. Because otters like to feed on shellfish, animals that play stone juggling more often are better at extracting food. However, when the researchers asked otters of different ages to solve food-related puzzles, the more juggling otters did not do better than other otters.

One possible explanation for the team suggests that otters play with stones when they are excited, perhaps when they are looking forward to eating. For captive otters, it is expected that the feeding time may be sufficient to get them excited and distract, so they can play juggling. Still, they still have no real way to prove it, so the mystery remains to be solved.

“Zoo visitors are often bewildered by the juggling of otters. Surprisingly, few studies have investigated why otters are so keen to play with stones,” Mari-Lisa Allison, lead author of the study, said in a statement. “Our research provides a glimpse into this fascinating behavior. While hunger may well be the driving force behind stone juggling, the ultimate function of this behavior remains a mystery. “